ALBERT

Notes: Summary In Perdita portalis, a ground nesting, communal bee, males are clearly dimorphic. The two male morphs are easily distinguished based on head size and shape into (1) a flight-capable, small-headed (SH) morph that resembles the males of other closely related species and (2) a flightless, large-headed (LH) morph that possesses numerous derived traits, such as reduced compound eyes, enlarged facial foveae and fully atrophied indirect flight muscles. The SH morph occurs exclusively on flowers while the LH morph is found only in nests with females. While on flowers, SH males are aggressive, fighting with conspecific males and heterospecific male and female bees, and they mate frequently with foraging females. Using artificial observation nests placed in the field, I observed the behavior of females and LH males within their subterranean nests. LH males are aggressive fighters; males attacked each other with mandibles agape, and male-male fights always ended in the death of one male. LH males are highly attentive to the reproductive behavior of females; they spend increasing amounts of time near open cells during cell provisioning, and mating only takes place immediately prior to oviposition when females are forming the accumulated pollen and nectar into a ball. Based on larvae reared to adulthood in the laboratory, the two male morphs occur in equal proportions. The behavior of males in closely related species, especially P. texana, and the origin and maintenance of male dimorphism are discussed.

Notes: Summary One aspect of behavioral ecology that has received considerable attention, especially by students of social insects, is the relative amount of energy invested by parents in the rearing of male versus female offspring. Sexual selection theory makes predictions about how individuals should allocate their total investment in the sexes. To test these predictions we must accurately quantify the relative “cost” incurred by a parent in the production of an average individual of either sex. Body weight ratios are the most common estimate of cost ratio, but the correspondence between offspring body weight and energetic investment on the part of the parent has rarely been determined. Calliopsis (Hypomacrotera) persimilis is a solitary, ground-nesting bee whose natural history makes it particularly convenient for studies of investment patterns and foraging behavior. Each day females construct and provision from 1 to 6 cells in linear, closely-spaced series. Each cell is provisioned with pollen from Physalis Wrightii flowers, which is collected on two or three foraging trips. However, the temporal sequence in which two- and three-trip foraging bouts occur is not random. Females invariably begin each day provisioning cells with three trips worth of pollen and usually switch to provisioning the latter cells of the day with just two trips worth of pollen. The sex of the offspring within the same co-linear series of cells also varies non-randomly — female offspring predominate in the first cells of each series and male offspring in the latter cells. The correspondence between the number of foraging trips to provision a cell, the total time spent foraging, and offspring sex was determined for 36 cells. The data indicate a close, though not absolute, relationship between the number of foraging trips and the sex of the offspring: males usually received two trips of pollen, though some received three, whereas female offspring invariably received three trips worth of pollen. A number of potential estimates of the relative cost of female and male offspring production were calculated. Estimates of the cost ratio based on the amount of time spent foraging, adult dry body weight, and pollen ball dry weight all give similar values. Female offspring receive an energetic investment of from 1.3 to 1.5 times that of males. These results support the use of adult dry body weight ratios in the estimation of cost ratios.